Impurities in pharmaceuticals are unwanted chemicals that remain with the Active Pharmaceutical Ingredients (APIs) or develop during formulation or develop upon ageing of both APIs and formulated APIs to medicines. In the pharmaceutical world, an impurity is considered as any other inorganic or organic material, or residual solvents other than the drug substances, or ingredients, arise out of synthesis or unwanted chemicals that remains with APIs. Impurity profiling includes identification, structure elucidation and quantitative determination of impurities and degradation products in bulk drug materials and pharmaceutical formulations. Impurity profiling has gained importance in modern pharmaceutical analysis due to the fact that unidentified, potentially toxic impurities are hazardous to health and in order to increase the safety of drug therapy, impurities should be identified and determined by selective methods.
Organic impurities are often free radicals from by-products, intermediates, or degradation products. Inorganic impurities include transition metals, reagents, and ligands.
The presence of these unwanted chemicals even in small amounts may influence the efficacy and safety of the pharmaceutical products. Different pharmacopoeias such as British pharmacopoeia (BP) and the United States pharmacopoeia (USP) are slowly incorporating limits to allowable levels of impurities present in the APIs or formulations.
The control of impurities in Formulated products and Active Pharmaceutical ingredient’s were regulated by various regulatory authorities like ICH, USFDA, Canadian Drug and Health Agency are emphasizing on the purity requirements and the identification of impurities in Active Pharmaceutical Ingredient’s (API’s).
Terms used by various regulatory bodies and ICH to describe the impurities as follows;
2. Penultimate intermediate
4. Transformation products
5. Interaction products
6. Related products
7. Degradation products
Methods to Identify the Impurities:
1. Reference standard method
Reference standards serve as the basis of evaluation of both process and product performance and are the benchmarks for assessment of drug safety. This method is not only for the active ingredients in dosage forms but also for impurities, degradation products, starting materials, process intermediates, and excipients.
2. Spectroscopic method
Spectroscopy methods are UV, IR, MS, NMR and Raman spectroscopy.
3. Separation method
The Capillary electrophoresis (CE), Chiral Separations, Gas Chromatography (GC), Supercritical Fluid Chromatography (SFC), TLC, HPTLC, HPLC are used for separation of impurities and degradation products.
4. Isolation method
Solid-phase extraction methods ; Liquid-liquid extraction methods ; Accelerated solvent extraction methods ; Supercritical fluid extraction ; Column chromatography ; Flash chromatography ;TLC ;GC ;HPLC ; HPTLC ;Capillary electrophoresis (CE) ;Supercritical fluid chromatography (SFC) .
5. Characterization method
Characterization methods highly associated sophisticated instrumentation, such as MS attached to a GC or HPLC, are inevitable tools in the identification of minor components (drugs, impurities, degradation products, metabolites) in various matrices. For characterization of impurities, different techniques are used; which are as follows;
NMR-Nuclear Magnetic Resonance Spectroscopy
The ability of NMR to provide information regarding the specific bonding structure and stereochemistry of molecules of pharmaceutical interest has made it a powerful analytical instrument for structural elucidation
It has an increasingly significant impact on the pharmaceutical development process over the past several decades. Advances in the design and efficiency of the interfaces, that directly connect separation techniques with Mass Spectrometers have afforded new opportunities for monitoring, characterizing, and quantification of drugrelated substances in active pharmaceutical ingredients and pharmaceutical formulations.